1947 Panel Truck Frame swap with ’88 k2500

[Second Series]

The only discrepancy I see is my truck uses pin 36 instead of 33, but they appear to have the same function.
Here is the truth table:

[Second Series]

From this I came up with this diagram.
I think it will work.

[Dan Bowles]

Originally Posted by Second Series

My k2500 is the 6-lug. Does the 8-lug k2500 have a wider tread? I read where someone swapped the 6-lug to 8-lug spindle and modified the upper A-arm, that’s my plan. The diffs are 3.73, the ’88 8-lug rear in the ’47 is also 3.73. I was concerned about how the rear works with the RWAL (Rear Wheel Anti-Lock) system. I don’t see any wires to the rear axle. The schematic show the VSS supplies the signal for that system, so it should be good to swap the rear.

My local guy swapped his completely over to 8 lug with little or no effort. Swapped spindles and the axle. I don't think there is a significant width difference. Anti-lock I think just was a speed sensor in trans for 88. Nothing high tech there and you can by-pass it by ripping out the ABS box and running brakes direct. Those things are probably failed by now anyway!

I'll get pics of Eli's truck soon. He's tearing stuff apart again working on some body work right now. It's been up and down over the last 10 years. A giant wheelbarrow full of storage for at least 6. The nice thing was getting a set of 93-94 extended cab bucket seats. They sit almost perfect on the riser and give you a flip forward/slide forward option on the passenger seat for rear access if you need. No major mounting issues, either because the frames are about square and flat unlike about every other front seat you run into!

[Second Series]

I have been reading build threads here and found a few full size frame swaps very inspirational.
I signed a contract and put a deposit down at the shop, now I’m waiting for space to open up so I can drive the trucks there. Once the build starts, I’ll need parts. I don’t know what all I will need, but some of it is obvious.
I created a spreadsheet of available parts. I started at one on-line parts catalog, and looked through each category. I picked what I think I will need and put it on the spreadsheet. I looked at a few sites, and was able to compare prices. I placed an order today for some parts with one company that is having a holiday sale.
I realize some things won’t be needed for awhile, like window gaskets, but I got some anyway. This was a small order, I may be more cautious in the future. Some parts are common to the suppliers, other parts seem to be at one or the other. It’s random. I am also looking through discussion threads about what parts to avoid, or who sells the best parts. This helped me choose the right outer rubber window seals.
There is a sale this holiday weekend at the wrecking yard. I’ll look for seats, a steering column, spindles etc. I’m committed to this build now. At some point I’ll have boxes of parts. I don’t intend to have boxes of parts waiting for years. I plan on going full speed ahead!

[Second Series]

I received one box of parts minus a few on back order. The back ordered parts arrived this week, but one part was off by a couple digits so I’ll have to wait until they get the right part in stock before I can return this. I spent some time in the wrecking yard, scored a couple front seats out of a Astro van for $40. I tried to get the front spindles off a k2500, but got burned out after two hours. I didn’t have the right tools, my time was running out, but what I mostly needed was a cheeseburger. On the way out I saw a barebones steering column in a jeep. I’ll try to get back there after work soon. Yesterday I ordered some bullet tail lights.
Two weeks ago I drove my panel truck for the last time, as it is, to the resto shop. This week I drove the ’88 GMC there, the panel truck was being dismantled and they hit me with a healthy bill. Today I got a call that the GMC bed has been removed and most of the panel truck parts are ready to get blasted. I thought I could recoup a little by hauling the extra parts off myself, but I don’t have the time, don’t want to pay to store them, so it’s off to the scrappers with the ’88 GMC bed.
I’m still trying to decide on the color. I had wanted a very dark purple that looks black, when I started driving the panel truck over 20 years ago. I still think that would be cool, but something subdued might be better for a daily driver. I’m considering two-tone grey, or grey and midnight purple. The resto guy said he likes to use the vintage colors on builds like this, but that it’s my decision. I have been looking at the vintage colors, but in 1947 the Forester Green was the standard. There were a handful of options, and two-tone wasn’t available until ’54 then it was just white for the top half. I recently went on a road trip a saw a couple vehicles with a light blue on the lower half and cream on top, that I like. So now I’ll think about the two-tone grey, and the blue and cream, and I have some model paint to play around with a dark purple.
My parts spreadsheet is growing and I need to order all the hard parts before any paint. I’ll add windshield washer nozzles for example, and whatever bits and pieces I can think of. I also need to continue engineering the ’88 wiring to the ’47 controls. I just read that the brake light switch has multiple contacts, so that will all have to function one way or another. Moving right along!

[Second Series]

One of the stipulations of the contract is that we meet once a week to go over progress, keep motivated, and settle up the bill. The panel truck body is almost free, and the donor truck is being picked apart.

[MiraclePieCo]

This is an exciting build. I really dig those 1-ton panels. I'll be watching!

[Second Series]

Each week I visit the shop, a little progress has been made. Last week the body was on a cart, and the two frames were side by side. Comparing body mounting points and deciding how to modify the donor frame. The ’47 gas filler is on the passenger side. 1988 the filler is on the driver side, tank is inside the frame rail. Pre ’88 the tanks were outside the frame and an auxilliary tank could be added to the passenger side. That doesn’t appear to be an option here, the ’88 auxiliary tank was behind the axle and I want the spare tire there. It could be done, re-route the exhaust to the driver side and find a tank with the passenger side filler. There is the driver side transfer case, so exhaust would go below that. I may go with moving the filler to the driver side on the panel. Here is a picture from a couple weeks ago…

[Second Series]

Little progress has been made since last week, but a little progress each week will get the job done. Fuel tank removed and exhaust cut. I have been researching how to use the stock instrument cluster and speedometer. I took the instrument cluster to hook it up to my ’90 chevy so I’ll have that working when this project is ready. I may be able to replace the 40 tooth reluctor in the transfer case tailhousing with a mechanical speedometer drive, and use a mechanical to electric pass through adapter for the DRAC. I’ll either build my own DRAC, or get one from a ’91-’94 truck. The ’88 DRAC is integrated in the display pcb…

[Purcell69]

I really like what you've got going. Like others have already mentioned, due to the newer frame configuration, you will either need to raise the body mounts or raise the floor of the truck to recess the frame in to it. Personally, I would build the body mounts up to work with the stock cab floor. That is what I did. I can't stand a truck with a bed that is only 6" deep. I use my bed and don't like the look of the "non-functional" bed, but that is just personal preference.

The other issue will be track width. Your tires will stick out past the fenders to some extent. Some of this can be minimized with wheel offset, but unless you go to lengths to widen the body or flare the fenders, the tires will stick out. With tall/skinnys on stock offset wheels, mine stick out about 1.5" per side. Again, this is personal preference.

Getting the wheelbase to fit the body is the biggest part of the battle and it looks like you have a good start on that. You may need to extend the front and rear of the frame for your body mounts, but that can be done with some 10 gauge steel.

Since you have the original frame, you can replicate the profile of the frame rails using square tube laid across the new frame and then build your body mounts from there. Again, this was how I chose to do it.

I think this will be a great daily driver when you are done. Unique, reliable and easy to work on and enjoy. None of that is wrong. I'm looking forward to see where this goes.

The red truck is a local. I don't know what specific chassis he used but it is 1973-1987 GM 4x4 K10.

-Joe

[Second Series]

Thanks Joe, I feel the same about the functionality of the bed. The panel truck bed will be as close to the frame as possible. The cab floor is lower than the bed and the donor frame is lower under the cab, so it should work good. It looks like the cab floor will be near the level of the top of the transmission, so no hump needed. I dig that red truck, I don’t think mine will be that high, one of the reasons I will not use a solid front axle. Not much progress this week, but the plan is to remove the rear end and build a body mount template out of 1” L-stock. You may notice in the picture in my previous post, the frame appears to be higher in the rear driver side, we’ll check that at the alignment shop. We’ll use the brackets and frame ends from the ’47 frame. The original frame had extensions on the rear.

[olcarguy]

Looking good so far...I like the one ton panel, a little longer then the 1/2 ton that I have. Keep up the good work, you will figure out the wires.....

[Second Series]

Thanks olcarguy. The frame bracket template is set in place, it needs a few tweaks to clear the front end, and one of the frame cross member will be replaced. The torsion bars are relaxed and the rear or the frame is now even, so the tension was causing the frame to twist. We will beef up the frame. The engine /transmission has been set aside to gain access to the frame work.

[Second Series]

Modifications have been done to the frame bracket template. It now clears the front end and the Z-axis points have been determined. I want the body to ride at or near stock height, so the 2” wood blocks won’t be used. The 2” hat channel cross sills will be replaced with 1x2 tubing layed flat. This will put the bed as close as possible to the frame. All other mounting points are lowered about 3” relative to the bed mounts. Now all the brackets can be tacked in place, and the body will be test fit.

[Second Series]

Progress is going slow this time of year, but little by little we’re moving right along. The ends of the ’47 frame are cut and being grafted to the donor frame. The rear frame extension is offset lower for two reasons. The body will be closer to the frame so the rear bumper will be lower relative to the frame, and there is a rear cross sill attached to the body that mounts on top of the frame. The front frame ends are narrower on the ‘47, we’ll move those out to match the donor and modify the bumper bracket. The bed wood is out and is in great condition, so I’ll probably keep it.
I have been researching how to run the original speedometer with the electronic system. I have a couple options. I could replace the tailhousing of the transfer case to use a speedometer cable. I would then use a mechanical to electric pass through adapter to get either 2000 pulse per mile, or 4000 pulse per mile. I would need to build a DRAC that works opposite of the original and get the 128ppm for the anti-lock, and 2kppm for ECM or 4kppm for cruise, but I don’t think I have cruise control, so 4kppm isn’t needed. The other option is to keep the system stock, DRAC is integral with the gauge cluster, so I’ll get a DRAC module from a ’92 to ‘95 and get the 2kppm signal to run a 12v motor to drive the mechanical speedometer, sure I could buy an electric to mechanical speedo drive, where’s the fun in that? I have found 3 different off the shelf solutions in the $300 range.
The mechanical speedometer can be adjusted to work with the rear gear ratio and the tire size. There are a few driven gear choices available for the np241, actually the 700R4 driven gear is used. There are 12 options with a range between 15 and 45 teeth. I may make a chart to compare driven gear, axle ratio, and tire size, unless anybody knows if one exists? If this isn’t right on and the ECM signal is being generated from it, there could be engine performance issues.
The electric speedometer is adjusted in the DRAC(digital ratio adapter controller). The tailshaft has a reluctor ring that generates 40 pulses per driveshaft revolution. The DRAC converts the 40 pulses to 128,000 pulses per mile, that’s 1:3,200 seems like a small margin for error. Before the 128k is generated, there is a circuit to set the diff/tire ratio. I’ll have to look at the charts on that. The 128k is divided by 32 to get 4kppm, and again ÷2 to get the 2kppm for the ECM. This just seems like a more precise way to generate the signal for the ECM, but I don’t know if it really matters or not how acurate the actual speed is compared to what the computer thinks?
The off the shelf electric to mechanical speedometer adapters have a way to calibrate the speedometer. This may be a redundant function, as it should be done in the DRAC. If the speed is not adjusted in the DRAC, the ECM may be getting the wrong information.
I took the motor out of a cordless drill, had some random transistors on hand and built a darlington pair for the supply. I have been playing around with motor controllers for awhile and have an arduino set up already, so I used that to for the speed control. The motor can run somewhat slow, but not slow enough. It works out to be at 2MPH the speedometer cable spins at 33.3rpm, and this motor looks like it is spinning faster than a record player. I’m looking for gears, or a different motor. Once I get the speed dialed in, I’ll work on the code to convert 2kppm to 1krpm.

[olcarguy]

Looking good....a little bit every day is a good thing...slow and easy wins the race.....

[Second Series]

I remembered to take some pictures this time. The frame ends and body mounts are tacked in place. The rear suspension is moved back. The plan is to measure everything again and bolt the rear in place. With the rear bolted in, we’ll roll it over to the alignment shop. After it’s dialed in, the rear hangers can be welded. I decided to leave the six bolt lugs for now. The 8 lug rear from the ’86 suburban is narrower between backing plates. I don’t know how the wheel mounting surface to wms compares to the ’88 6 lug. The 8 lug rear could fit with some modification. This can be done later, as now I must focus on the best use of funds to keep the project moving.

[Second Series]

The body mounts are tacked in place and the engine is back on the frame.. A few bed boards are being used to locate the new 1” cross sills(1x2 tube). Next step is to mock up the body on the frame.

[Rusti]

Very interesting way to work with a second frame.
So Long
Arnd

[Second Series]

The body is on the donor frame, it has a 2x4 under the front in the picture, still needs some adjustments. The bottom of the firewall above the transmission will be modified. The rear of the rear inner wheel well will be trimmed to accommodate the leaf spring. The 1x2 cross sills have the bed as low as it can go without major mods.
The next step is to hang the fenders, start carving the front inner fenders, and locate the running board brackets. The front and rear running board brackets have conflicts, so will need to be moved. The radiator will need to negotiate it’s placement based on the location of the steering gear. I got a desert cooler radiator 25+ years ago, it should be good for this 350. I’m just not sure about the horizontal vs. vertical flow.
I’m still working on the motor drive for the mechanical speedometer. I found a motor with the right range, now I’m working on the code to convert frequency to PWM. I also need a DRAC module since my DRAC is incorporated into the gauge cluster pcb. I went to a scrapyard yesterday, but all the trucks had the electronics removed.
It was a good feeling to see the body on the frame, this is a good milestone in the build. There is still a long way to go, but this is a positive turn.

[Second Series]

Originally Posted by Rusti

Very interesting way to work with a second frame.
So Long
Arnd

I have know the frame can be cut and lengthened or shortened. This kind of frame has a C-channel back into a boxed front. That joint can be cut and the length modified. I thought the rear axle could simply be moved back, so that's how we went, and then add extensions to the front and back to lengthen the frame.
I had read about someone using plywood for the body mounts locations when doing a frame swap, another suggestion was metal. We had some issues with the metal template, interfering with the donor front suspension, modified that. Then the running board part was too narrow so we had to raise up the template. It got the job done.

[Second Series]

Back on this. The rear fenders are set in place, and the runningboard brackets placement are being located. You can see where the Mr. Peanut was removed from the side, and the 5¢ on the door. The rear tire is inside the fender, I’m curious how the front tire will be. The rear wheel might could be moved ½” forward to center in the wheelwell. I didn’t measure, but it looks like the distance from the top of the tire to the wheelwell is close to the 4” = stock height. In my preliminary plans I figured the stock height could be preserved if we removed the 2” wood blocks, and replaced the 2+” hat channel cross sills with 1x2 tube. After teardown and using the body/frame template, we thought it would have a 2” lift. Now that it’s coming together, things are lining up well. There is plenty of clearance between firewall and engine. The firewall had to be modified just above the transmission, but not much. Next steps are to attach the runningboard brackets, modify the front inner fenders. Once the front fenders are in place, the core support will be addressed.

[Second Series]

I like how the front tires don’t stick out of the fenders, they are just inside. I may be able to run wheels with a greater positive offset to suck the tires in. The fan and fan clutch are being greedy in the core support area. We’ll get the grill and support panel mocked up and see how a radiator will fit.

[Purcell69]

Originally Posted by Second Series

I like how the front tires don’t stick out of the fenders, they are just inside. I may be able to run wheels with a greater positive offset to suck the tires in. The fan and fan clutch are being greedy in the core support area. We’ll get the grill and support panel mocked up and see how a radiator will fit.

Have you considered running a two speed electric fan? When I put Ethyl on the 1994 Dodge chassis, I was concerned about space up front, so I moved the engine and transmission 3" back, which was about as far back as I could go with the 1957 firewall. This of course snowballed things a bit, in that I needed to have a new front driveshaft built to add in extra length. I still went with two speed electric fan from a 1995 Ford Taurus V6, the same one the rock crawling guys use in their Jeeps. Those things move an honest 4000 cfm in high speed mode. In the end, I have more room up front which made building a lower radiator hose easier.

I'm impressed with the build. You've really done your homework as far as getting things to fit. It really is a good feeling seeing the body on the frame for the first time. I used 3/16" plate steel to make my body mounts, for what it is worth.

-Joe

[joedoh]

I hope you find some wheels that are higher offset, those stockers are already pretty high offset!

looking great !